The present invention relates to integrated circuits and packaged integrated circuits and, more particularly, to a leadframe for packaged integrated circuits.
An integrated circuit (IC) die is a small device formed on a semiconductor wafer, such as a silicon wafer. A leadframe is a metal frame that usually includes a paddle that supports an IC die that has been cut from the wafer. The leadframe has lead fingers that provide external electrical connections. That is, the die is attached to the die paddle and then bonding pads of the die are connected to the lead fingers via wire bonding to provide the external electrical connections. Encapsulating the die and wire bonds with a protective material forms a package. Depending on the package type, the external electrical connections may be used as-is, such as in a Thin Small Outline Package (TSOP), or further processed, such as by attaching spherical solder balls for a Ball Grid Array (BGA). These terminal points allow the die to be electrically connected with other circuits, such as on a printed circuit board.
The lead frame is usually formed of copper or nickel alloy. One way of attaching the die to the die paddle is by soldering. High power devices require extremely high temperature solder die attach (about 300° C.) and device reflow (about 260° C.). However, at high temperatures, the leadframe plating is degraded, which affects the wirebonding process. More particularly, the bondability of gold wire is affected due to the metallurgy change of the plating surface and by solder flux contamination. Further, a thick die paddle is preferred for high power devices to facilitate heat dissipation. However, singulation (saw or punch) of a leadframe formed of very thick metal is difficult and not reliable.
It would be desirable to provide a lead frame that provides good heat dissipation yet is not difficult to singulate. It further would be desirable to be able to attach a die to a die paddle with a high temperature process that does not cause defects.